STM32f103c8 ADC error, Constant error value( 1.69 Volt) and erratic output

[VVish.2]

I am trying to create ADC using STM32F103C8. Software i am using are:

a. STM32CubeMX

b. Keil Vision -- V5

c. Hercules to Monitor the Serial Output

Clock Setting of STM is 72 Mhz and 12 Mhzfor ADC

Code :-

while (1)

 {

   /* USER CODE END WHILE */

      HAL_ADC_Start(&hadc1);

      HAL_ADC_PollForConversion(&hadc1,300);

      raw = HAL_ADC_GetValue(&hadc1);

      float vin = (double)raw*(3.3/4096);

      sprintf(msg1,"Vol = %.2f , HEX Value = %.4x \r\n",vin, raw);

      HAL_UART_Transmit(&huart1,(uint8_t*)msg1,sizeof(msg1),300);

   HAL_Delay(1000);

   /* USER CODE BEGIN 3 */

 }

i am getting a constant DC Output of around 1.69 Volt, when input volt at ADC is Zero (Screen Shot attached). After supplying any Voltage value between 0 - 3.3 Volt, output is varying contentiously between 0 to 3.3 Volt.

I have checked the input reference volt, it is 3.3 Volt. Can you suggest me how to resolve this issue. I have printed a HEX value of output of function HAL_ADC_GetValue(&hadc1).

[waclawek.jan · Accepted solution]

> i am getting a constant DC Output of around 1.69 Volt, when input volt at ADC is Zero

I guess, you've left the input floating (unconnected) - ADC output is then undefined.

Zero input means, that the input is connected to ground.

JW

[VVish.2]

Thanks for the Reply. Your suggestion work perfectly.